Magnetic recording media are widely used as recording tapes, videotapes and floppy (a registered trademark) discs, and generally they take the structure comprising a magnetic layer laminated on a support. Magnetic recording media are required to be on a high level in various characteristics, e.g., electromagnetic characteristics, running durability and running performance. That is, in audiotapes for recording and reproducing music, higher reproducing capacity of original sounds is required. Moreover, videotapes are required to be excellent in electromagnetic characteristics, such as excellent in reproducing capacity of original images. Magnetic recording media are also demanded to have good running durability concurrently with excellent electromagnetic characteristics.
In recent years, with the increase of recording capacity and density, higher output and higher sensitization of a magnetic layer are increasingly required. Under such a tendency of the times, thinning of a magnetic layer has been advanced and a magnetic recording medium comprising lamination of an intermediate layer provided between a support and a magnetic layer is proposed. In particular, for the purpose of realization of good electromagnetic characteristics and running durability, a magnetic recording medium having a smooth and thin magnetic layer having high film strength is desired and, e.g., a magnetic recording medium having a magnetic layer containing a poly-urethane resin having a glass transition temperature of from 100 to 200° C. as a binder and minute spines (projections) on the surface having heights of from 10 to 20 nm restrained in number is proposed (e.g., refer to JP-A-2003-123222 (The term “JP-A” as used herein refers to an “unexamined published Japanese-patent application”.)).
The state of a˜magnetic layer surface is very important for recording and reproducing. A phenomenon that a signal comes out in recording and reproducing, i.e., so-called dropout (DO), caused by the adhesion of dusts on the surface of a magnetic layer, agglomerates of magnetic layer components, unevenness due to scratches on the surface of a magnetic recording medium and other defects brings about the deterioration of recording information. In particular, in a magnetic tape, e.g., a videotape, in a wound state, a magnetic layer is in contact with the back surface of the magnetic recording medium directly, so that so-called “offset”, i.e., a phenomenon that the ruggedness of the back surface is impressed upon the magnetic layer, is liable to occur and problematic.
As a means for reducing the phenomenon of offset, strengthening a thinned magnetic layer and preventing the deformation by aging, a method of adding a hardening agent to a magnetic layer has so far been used (e.g., refer to JP-A-2003-30814).